I would like to share my findings in case someone else encounters a similar issue after upgrading to Unraid 7.3.1.

System Information

• Motherboard: ASRock IMB-X1316

• Boot device: Samsung FIT 64 GB USB flash drive

• UPS connected via USB: APC Back-UPS BX950MI

• Previous Unraid version: 7.2.5

• New Unraid version: 7.3.1

• Original BIOS version: P1.10 (2023-10-11)

Symptoms

After upgrading from Unraid 7.2.5 to 7.3.1 and rebooting, the server never came back online.

Connecting a monitor showed that the system was hanging during the boot process. The boot files were verified successfully, but shortly afterwards USB-related errors appeared:

usb 1-11: device descriptor read/64, error -110
usb 1-11: device descriptor read/64, error -71
usb 1-11: Device not responding to setup address.
usb 1-11: device not accepting address, error -71

This was followed by storage errors involving the boot device:

I/O error, dev sda
device offline error, dev sda
FAT-fs (sda1): FAT read failed

Eventually Unraid failed to mount required boot components:

SQUASHFS error: Failed to read block 0x0
unable to read squashfs_super_block
cannot mount /boot/bzfirmware

At this point the boot process stopped.

Initial Workaround

After searching for similar issues, I moved the Samsung FIT boot drive from its original USB 2.0 port to a USB 3.x port on the rear I/O panel.

The server immediately booted successfully.

At first I suspected:

• a failing flash drive,

• a damaged USB port,

• or a corrupted update.

However, further testing did not support those theories.

Investigation

While running successfully from the USB 3.x port, lsusb -t showed:

Bus 001:
  APC UPS
Bus 002:
  Samsung FIT USB flash drive

The system logs were completely clean after boot. No USB resets, disconnects, or storage errors were present.

I then moved the boot drive back to the original USB 2.0 port and rebooted.

The failure returned immediately.

Moving the drive back to the USB 3.x port allowed the system to boot again.

This behavior was fully reproducible.

BIOS Discovery

During troubleshooting I noticed that the motherboard was still running the original release BIOS:

Version: P1.10
Date: 2023-10-11

ASRock has released several newer BIOS versions since then.

I updated the motherboard BIOS directly to version P1.80.

After the update, I moved the boot drive back to the original USB 2.0 port and tested again.

Result

The BIOS update did not cause any problems and it well fairly easily.

The problem disappeared completely.

The system now boots normally from the same USB 2.0 port that consistently failed before the BIOS update.

Multiple reboots have been successful.

Conclusion

In my case:

• The Samsung FIT flash drive was not defective.

• The USB 2.0 port was not defective.

• The Unraid installation was not corrupted.

The root cause appears to have been a compatibility issue between:

• the newer Unraid 7.3.1 kernel,

• the motherboard’s USB/xHCI implementation,

• and the original P1.10 BIOS.

Updating the ASRock IMB-X1316 BIOS from P1.10 to P1.80 completely resolved the issue.

If anyone experiences USB enumeration errors, disappearing boot flash drives, or cannot mount /boot/bzfirmware messages immediately after upgrading to Unraid 7.3.1, it may be worth checking whether a motherboard BIOS update is available before replacing the flash drive or other hardware.

Hopefully this helps someone save a few hours of troubleshooting.

Thank you for this, I also encountered the this issue and the behavior is exactly the same for me. I upgraded from 7.2.4 and the system would not boot on a USB2.0 port with the error message you described but without issue from a USB3.0 port.

Unfortunately, there is no BIOS update for my motherboard available at the moment, so I will probably go back to 7.2.4 for now.